The present invention relates to a helicopter with a turbine power unit fitted with an exhaust screening device. A major design problem on military helicopters is how to minimise heat emission to the outside atmosphere, for eluding enemy missiles with automatic infrared-ray homing systems.
Solving this problem is especially vital when the helicopter rotor is powered by a tubine power unit, the trail of hot exhaust gas from which is a veritable "approach run" for infrared-ray missiles, and the exhaust nozzles of which provide a perfect target.
A first approach towards solving this problem on known military helicopters with turbine power units consisted in extending the turbine exhaust nozzle by means of a tubular screening device having movable or fixed transverse blades arranged in such a manner as to prevent the "eye" of the exhaust nozzle from being directly visible from outside.
Subsequently, attempts were made to lower the temperature of the exhaust gas by mixing it with outside air inside the screening device. This was achieved by fitting the inside of the screening device with tubular transverse blades communicating, at the end, with the outside atmosphere and, centrally, with the inside of the screening device, and by exploiting the vacuum produced by the expanding exhaust gas from the screening device, for drawing cold outside air into the screening device through the blades.
The major drawback of the above known solutions is that the amount of exhaust gas cooling provided for is insufficient for eluding the increasingly sophisticated homing system on modern missiles.
The main reason for the relatively poor performance of known screening devices is that the air stream sucked in from outside through the said tubular blades is insufficient for cooling the temperature of the exhaust gas as required.
Furthermore, known screening devices consist of passive elements which reduce the carrying capacity of the helicopter, firstly, on account of the relatively heavy weight involved and, secondly, by determining exhaust coounterpressures resulting in considerable power loss on the respective power units.